The Star Wars universe provides hundreds of species which are feasible for characters (essentially all humanoids and even more). In terms of star wars lore (be it canonic, expanded-univere or from other origins) there is tons of information, background stories, unique traits, skill, culture etc.
For the rest of this question I will assume that it is desirable to have a party or parties which consist out of a variety of different species, which--for me--contributes an important part to the liveliness and the space-opera-feel of the Star Wars Universe
In Star Wars D6 however, alien races which players choose will essentially only influence the minimal and maxmial values of the 6 base attributes. For example while humans (and also many species) must have starting attributes betweend 2D and 5D for some alien species this shifts to 3D to 6D with some attributes.
Given the starting number of dies to distribute, this change in minimal and maximal attribute starting values has only a very limited effect: unless you are building a highly specialized characters (say a wookie which is immensly strong and wants to start with 6D on STR) alien characters look--from a rules perspective--just like humans, and are indistinguishable from each other.
Other systems use things like advantages/disadvantages or species-specific traits (like night vision, ...). But Star Wars D6 does not provide for a rules-system way of doing this, so we introduced our own advantages/disadvantages mechanic at character creation.
How did you make different alien species feel unique and special to your players? (Assuming that having not all players play the same old boring humans is a good thing. :) )
How do you handle canonical traits which give certain species a clear advantage over others? (Some species have underwater breathing for example--which the characters get 'for free' by just picking said species.)